1. Field of the Invention
The present invention relates to a method of generating plasma in a liquid and an apparatus therefor.
2. Description of Related Art
Conventionally, the deposition technique with vapor phase plasma is widely made use of as a deposition technique with the use of plasma. For example, JP-A-10-81589 describes formation of a diamond film on surfaces of silicon or cubic silicon carbide with the plasma CVD method. However, with such method, it is difficult to compose a large amount of deposited substance. When a source material such as methane, etc. is quickly supplied in order to increase the deposition rate, there is a fear of incurring a danger. Also, when high-energy plasma is generated in vapor phase, the temperature rises and it is not possible to perform deposition on a substrate material having a low degree of heat resistance.
On the other hand, formation of submerged plasma by ultrasonic cavitation and superposition of local electromagnetic fields described on page 56 of the proceeding in Fourth All Ehimê University Symposium is based on an exceedingly promising thought directed to generation of plasma in a liquid, but the document and the presentation present a principle at the start of such study and in no way describe how to concretely carry out such formation.
Subsequently, conventional methods of garbage disposal are described. It is general to burn garbage in an incinerator to discharge exhaust gases to the atmosphere after soot particles are removed by an electric precipitator or an adsorption filter. There have been tested a method of absorbing and removing gaseous dioxin present in exhaust gases by blowing-in of active carbon and an active-carbon adsorption tower, a method of decomposition removal by the use of a catalytic conversion tower, but these methods of removal involve problems in that after-treatment is necessary and the effect of treatment is dependent upon temperatures. That is, decomposition of dioxin is performed in high-temperature combustion reaction and so is exceedingly reduced in decomposing ability in the case of low combustion temperature. Also, in currently leading methods with the use of a bag filter, it is likewise necessary to perform treatment of decreasing gaseous dioxin in toxicity after the treatment of exhaust gases. Also, Polychlorinated Biphenyl (PCB), which has been used as an insulating oil for transformers in the past, is also accumulated and stored in large amounts because of the absence of effective processing means.
Also known is a method of decomposing dioxin, in which electromagnetic waves are irradiated on a liquid containing dioxin while the liquid is dripped so that plasma is generated for decomposition (for example, JP-A-2002-336650).
Conventional methods of treatment with the use of an incinerator involve a problem of the necessity of the treatment of finally making dioxin harmless. However, dioxin and PCB are substances, decomposition of which is exceedingly difficult, and even if it is possible to experimentally decompose a small amount of such substances, it is difficult to treat them in large amounts. A technique described in JP-A-10-81589 has its limit in rate of treatment when a liquid is decomposed while it is dripped. Accordingly, there are desired chemical reactors and methods of cracking treatment, in which such harmful substances are effectively decomposed and can finally be made harmless. Also, it is desirable to realize chemical reactors capable of effectively composing those substances, such as diamond or the like, which cannot be composed only at high temperature/high pressure.
It is an object to provide a submerged plasma generating apparatus and a submerged plasma generating method, in which high-energy plasma, which is macroscopically easy to handle at low temperatures is generated by generating plasma in a liquid. It is also an object to provide a technique that is capable of effectively performing decomposition of harmful substances, which are difficult to decompose, and composition of substances, which are difficult to compose, with the use of submerged plasma having a high energy.